Year	mmol per litre
1980	4.368
1981	4.363
1982	4.358
1983	4.354
1984	4.348
1985	4.344
1986	4.338
1987	4.33
1988	4.319
1989	4.311
1990	4.306
1991	4.302
1992	4.301
1993	4.301
1994	4.304
1995	4.308
1996	4.313
1997	4.321
1998	4.33
1999	4.341
2000	4.357
2001	4.375
2002	4.394
2003	4.416
2004	4.439
2005	4.463
2006	4.488
2007	4.513
2008	4.536